1. Technical Field
The present disclosure relates generally to color measuring apparatus with a measurement assembly which includes at least one illumination assembly for applying preferably substantially parallel illumination light to a measurement spot of a measurement object and a pick-up assembly for capturing the measurement light radiated back from the measurement spot and for converting the same into corresponding electrical signals. The disclosed color measuring apparatus can be formed as autonomous apparatus or as measurement periphery for employment in connection with a controlling computer evaluating measurement data independently of the underlying measurement technology. Autonomous color measuring apparatus generally include all of the control and display organs required for the measurement operation as well as their own current supply and moreover are frequently also equipped with an interface for communication with a computer, wherein both measurement data and control data can be exchanged with the computer. Color measuring apparatus configured as measurement periphery usually do not have their own control and display organs and are—like each other computer peripheral—controlled by a superordinated computer. For communication with a computer, modern color measuring apparatus are often, e.g., fitted with a so-called USB (Universal Serial Bus) interface, via which the current supply can also be effected at the same time in many cases (from the connected computer).
2. Background Art
Nowadays, metallic colors and varnishes with effect pigments are more and more employed not only in the automotive industry. Such colors exhibit a severe angular dependency. Varnishes with aluminum flakes for example exhibit a severe brightness flop. Varnishes with interference effect pigments additionally also exhibit color differences with varied observation or illumination direction. For measuring such varnishes, multi-angle measuring apparatus have been established. The gloss measurement is a related issue, in which the measurement result is also sensitive to angle.
Measuring apparatus which are able to acquire such characteristics have to be adapted to illuminate the measurement object in one or more different, exactly defined illumination directions (nominal illumination directions) and to pick up the light radiated back from the measurement object from at least one exactly defined observation direction (nominal observation direction). Observation direction and illumination direction can be exchanged. Color measuring apparatus of this type are, e.g., described in great detail in the documents EP 2 703 789 A1 and EP 2 728 342 A1.
In the publication “Geräteprofilierung: Management globaler Farbkonsistenz” of Wilhelm H. Kettler, DFO Tagung Qualitatssicherung und Prüfverfahren, 2008, various causes are set out, which can result in measurement errors in the employment of such color measuring apparatus. In particular, the so-called systematic errors, which are attributable to certain apparatus imperfections such as erroneous calibration belong thereto. In a lecture delivered by Wilhelm H. Kettler for Farbe und Lack II Seminare Modul 2: Tiefere Einblicke in die Farbmetrik Jun. 25-27, 2014, Stuttgart (FPL) with the title “Farbmanagement”, the so-called angular errors are in particular also indicated, which can arise by the geometric conditions of the illumination and observation beam paths as well as by the apertures of the illumination and observation beam paths. Angular errors especially effect particularly severely in the measurement on samples with effect colors.
The present invention primarily deals with avoiding and compensating for measurement errors caused by such angular errors, respectively.
Therefore, by the present invention, a color measuring apparatus of the generic type is to be improved to the effect that angular errors can be simply corrected such that the illumination and observation directions preset by the respective measurement geometry are exactly complied with and thereby measurement value corruptions are avoided.
This object underlying the invention is equally solved by the color measuring apparatus according to the invention characterized by the features of the independent claim 1 or by the features of the independent claim 14. Advantageous configurations and developments of the color measuring apparatus according to the invention are the subject matter of the dependent claims.